1. Field of the Invention
The present invention relates to a hard disk cache device and method, and more particularly, relates to a hard disk data read/write using at least one flash memory as a hard disk cache buffering device and method thereof.
2. Description of the Related Art
Accordingly, in prior art, hard disks are widely used for data read/write and as storage devices in mainframe computers or consumer electronic products, such as desktop computers, laptop computers, industrial computers, playback-featured DVD players, and other electronic products. However, considering hard disks consume a great deal of power usage, utilizing flash memory as a hard disk cache to perform major data read/write reduces power consumption and therefore achieves the purpose of energy saving. The technologies as reflected in the article “Flash Memory File Caching for Mobile Computers” which appeared in “Proceedings of the 27th Annual Hawaii International Conference on System Sciences” by B. Marsh, F. Douglis, P. Krishnan, et. al., and Microsoft Corporation publication of “Hybrid Hard Drives with Non-Volatile Flash and Longhorn” and prior art cache management mechanism are noticed. In addition, another publication of “Computer Architecture: A Quantitative Approach”, published in 1996 by John L. Hennessy and David A. Patterson of Morgan Kaufmann Publishing company, noticed that direct mapping or method of “Set Associative” cache, is great for consideration within Academia, but not applicable for using flash memory as a hard disk cache.
In consideration of flash memory as a hard disk cache in prior art, the logical address space corresponding to the flash memory is much greater than the physical address space of the flash memory. Therefore, the prior art flash memory storage system technologies and management mechanisms, e.g. Aleph One's YAFFS (Yet Another Flash Filing System) technology or M-Systems' NFTL (Flash-memory Translation Layer for NAND flash) technology are not applicable. In addition, these prior art flash memory cache system technologies and management mechanisms lack a data replacement mechanism in cache, so that it cannot be directly used as a hard disk cache management mechanism.
As noted above, in the year 1994, Marsh et. al., used flash memory as a hard disk cache in order to achieve the purpose of saving energy; however, they used in the original experiment a small storage capacity of a 40 MB hard disk, in addition to a 20 MB NOR-type gate flash memory from old computer components, which then is unsuitable to the current GB (giga-byte)-sized large storage capacity of hard disk or large storage capacity of NAND-type flash memory devices. In addition, in the technology published by Marsh et. al., “Flash Memory File Caching for Mobile Computers,” it does not mention how to effectively identify and locate the required data in the flash memory cache. The technique of identifying and locating the cached data effectively is not a problem when the flash memory capacity is small; however, when the flash memory capacity is in the tens and hundreds of gigabytes, effectively identifying and locating cache can be very important. The prior art of Marsh et. al., is not demonstrating the use of this.
Since 2003, Microsoft and Samsung began cooperating in the prototype technology of developing flash memory as a hard disk cache, that is, flash memory and hard disk to form a mix-component hybrid hard disk, called a hybrid hard drive. However, the hybrid hard drive prototype flash memory is used for write-only and as temporary boot data storage; as for reading data, it does not require a cache process. The hybrid hard drive only manages the data write cache, and the data read cache is managed by a new generation of Microsoft operating system software. The drawback occurs when used with non-Microsoft operating systems computer mainframe or electronic products, such as UNIX operating system or the mainframe computer using Linux operating system or other industrial computers and DVD player recorders, that it is unable to use the technology. This type of data separation to read or write cache management of prior art is effecting the efficiency and speed of hard disks, and inevitably affecting the frequent access of cache.